Pressurizing air systems within gas turbine engines provide bleed air under pressure for many purposes including supplying auxiliary power, cooling air, etc. A pressurizing air system may extract bleed air from a compressor of the engine at more than one stage thereof to obtain air flows having different temperatures and pressures, in order to meet requirements for different purposes within the engine. However, for gas turbine engine operations the bleed airflow changes in both temperature and pressure at the individual stage ports of the compressor. For example, the temperature and pressure of the bleed air at the individual stage port of the compressor increase when the engine is operated at a full power level in contrast to an idling condition. In another example, as the demand of a bleed airflow extracted from a particular stage port of the compressor increases, the air pressure and temperature delivered from this particular stage port of the compressor will decrease. All these factors will result in fluctuations and variations causing transient thermal stresses on the engine components and transient rubbing (pinch point) in the non-contact air and air/oil seals.
Accordingly, there is a need to provide an improved pressurizing air system for gas turbine engines to provide bleed airflows with relatively stable temperatures and pressures under most engine operating conditions.